Incandescent electric lamp



March 17, 1931. G, MlN 1,196,468

INCANDESCENT ELECTRIC LAMP '7 Sheets-Sheet 1 Filed June 28, 192B 040 yslagr March 17, 1931.

G. MAIN INCANDESCENT ELECTRIC LAMP Filed June. 28, 1928 7 Sheets-Sheet 2 6 Waff) March 17, l193. G, MA|N INCANDESCENT ELECTRIC LAMP Filed June 28, 192s '7 Sheets-Sheet 3 March 17, 1931.

G. MAIN ICANDESQENT ELECTRI C LAMP Filed June 28, 1928 '7 Sheets-Sheet 4 6- Wam /NveNTo/Z 3),/ 0mm/1 M@ March 17, 193.1. G. MAIN INCANDESCENT ELECTRIC LAMP 'r sheets-sheet 5 Filed June 28, 1928 v om A com

of o so* 4o; PN o l 0% on 1/ com NN ...8 oOm Il R f www l LN. \Q con m Q f .l .1 n a o? se .own com. o@ u. v w QA lllllhwfll.. eoo` .GxN l o o: X x E n 3v o2 uomv Sv omwroo March 17, 1931. Q MA|N INGANDESCENT ELECTRIC LAMP Filed June 28, 1928 '7 Sheets-Sheet 6 March 17, 1931- G. MAIN INCANDESCENT ELECT'RIC LAMP Filed June 28, 1928 '7,Sheeis-Sheet 7 Patented Mar. 17, 1931 GEORGES MAIN, or PARIS, FRANCE INCANDES CENT ELECTRIC LAMP Application filed June'28, 1928, Serial No. 288,845, and in France July 26, 1927.

The invention relates to incandescent elec.-

tric lamps of the vacuum or the gas type, and

Attempts have been made to attain suchV uesults by surrounding the lamp by reflectors or glass diifusers provided with prisms, or

reflectors of polished metal'forming projectors, or further, by silvering or enamell'ing certain parts of the lamp. However, all such methods have proved insufficient, and the resulting efficiency was always low, since it is inmossible to design reflectors of the proper shape in connection with an illuminant (incandescent filament) which differs much from a. point source of light.

An incandescent electric lamp according to flieinvention comprises in combination a lamp bulb having an internal reflector whose shape is such that each point of the incandescent filament acts as a point source of light relatively to the adjacent surface of the reflector, (otherwise stated, the said refiector, instead of having a'single optical centre, possesses a plurality of optical centers, the corresponding points of the lila-ment being cen;

` tei-ed with respect thereto) and /or more outer reflecting members adapted to deect the luminous rays emitted by said lamp toward the plane to be illuminated with such a concentration of luminous flux that the intensity of light in each direction is inversely proportional fo the cube of the cosinus of the angle formed by said direction with the perpendicular to said plane. In this manner I amen- 4() abled to direct the rays of light in the proper direction, and also to concentrate the light in the desired proportion, i. e. I afford the optimum distribution of the light which corresponds to the uniform illumination of the surface to be lighted.

The invention further relates to a specific lamp of this kind, especially designed for the lighting of roads, streets, avenues, railway station platforms, and other rectangular surfaces of limited width.

Further characteristics of the invention will be specified in the following description.

In the appended drawings, which are given solely by way example:

Fig. 1 is a diagrammatic view showing the polar curve of a point illuminant, either alone or combined with an external reflector.

Fig. 2 shows the polar curve of a lamp with horizontal spiral filament ofthe known type.

Fig. 3 shows the polar curve of a lamp with sawl tooth or zigzag filament.

Fig. 4 shows an incandescent lamp provided with an internal reflecting screen or reflector.

Fig 5 shows the polar curve which is obtainedby the use of an internal screen, said screen consistingI of opal glassA and having the shape of a half-torus.

Figs. 6 to 10 show the curves obtained with internal screens of various shapes.

Fig. 11 shows the combination of a lamp with directed light, with an external reflector.

F ig, 12Ais a view which shows the polar curves to be obtained in the longitudinal and the transverse .direction in order to provide for a practically uniform illumination upon a rectangulaisurface.

Fig.Y 13 is a section on the line Iii-13 ofv Fig. 14, showing a lamp with directed li ght, provided with an external reflector for the lighting of elongated rectangular surfaces.

Fig. 14C is a side view of the same.

Fig. 15 is a sectional view on a larger scale of the reflector and lamp on the line 15-15 of Fig. 16, and

Fig. 16 is 'a sectional view of the lamp on the line 16-16of Fig. 15.

Fig. 1 shows the polar curve P1 of an illuminant which is supposed to be concentrated at a point O; this curve is a circle whose radius O A represents the mean spherical intensity, which has the same value according to the different angles 10, 200, 30, etc., starting from the vertical.

If the said illuminant O is placed within a reflector such as R, of the standard type, this produces a new polar curve P2, wherein the luminous intensity at different angles,

0 B O 0 h2 3 0 10 -OWB C,lies-@0,955 00 o 0B cos3 20o OD o 0 B cos3 30 0 E If E@ denotes the illumination desired on the working plane and if it is supposed that 150:1 and L=1 meter, it is observed that, in order to obtain a uniform lighting at B, C', D, E, the luminous intensities must be:

1 l l OB-l 0O0,955 0D 0,83 0E 0,65

The desired polar curve of equal illumination on the plane to be illuminated is represented at P3 in Fig. 1. It will be seen that this curve is very different from curve P1.

In the preceding` considerations, it is supposed that the illuminant consists of a point, and that the polar curve is a circle, but, in the known lamps, the said curves have the shapes shown in Figs. 2 and 3. Such curves, as well as the curves P1 and P2 of Fig. 1, can only afl1 ord a uniform lighting when the snrface to be illuminated is a sphere, which condit'on is never fulfilled in practice, since the surfaces to be illuminated are generally flat or have no pronounced relief.

curve substantially coinciding With curve P3 may be obtained by the combination with the electric bulb of internal and external refiectors of suitable shape and relative arraiuement. as explained hereunder.

Fig. -l shows a bulb lnwingl an internal reflector for use in the lamp according to the invention. 1 is the incandescent filament, which has or has not a spiral shape, and is arranged in a circle; 9. is the reflecting screen, which may consist of polished metal or opal glass. or may comprise reflecting prisms. It will be observed that, since the screen is well centered `relatively to the filament 1, each point of said filament will act as a point source of light relatively to the corresponding part of the screen, whereby a well determined distribution of the light will be obtained. In other words, the luminous flux will be maximum in certain predetermined directions.

Such directions will be selected according to the particular application in view.

'i Thus, in Figs. 5, fi, 7, 8, 'the internal reflector or screen (having respectively the shape of a half torus, of a lower quarter of torus, of an upper quarter of torus, and of a double cone) will provide for the maximum light at an angle of D-T50 from the vertical. In the case of the known lamp with horizontal filament (Fig. 2) the maximum intensity is obtained at an angle of D with the vertical (radius O C) whilst, in the case of the spiral saw-tooth filament shown in Fig. 3, the maximum intensity is at O (radius O A).

Fig. 9 shows by way of example a modification in which the lamp with its reflector or screen is disposed for indirect lighting, the 'lament being entirely concealed by the lamp, the blinding effect is eliminated.

Fig. 10 shows another arrangement of the screen for direct lighting.

Considering again the bulb with internal reflector shown in Fig. 4, the polar curve 0btained with the said bulb is shown at PL in Fig. 11, and herein the maximum illumination is obtained at 550.

By comparing this curve with the curve Pg of Fig. 1, the improvement in the uniform illumination of the plane to be illuminated is clearly apparent. However, this effect may be still further improved by the use of external annular reflectors, so shaped and a1- ranged as to practically obtain the curve P;l (Figs. 1 and 11) which constitutes the optinunn polar curve.

The method of designing such annular rciiectors is as follows:

First, by photometry measures (according to the known methods of Rousseau, Bloch and others), I determine the luminous intensity in the various directions, and then the values of the elementary luminous 'linx in the different spherical regions comprised in the angles 0 to 100, 10O to Q00, 200 to 30o ete. whence I deduce the total luminous liu): of the lamp.

In the graphic representation, the intensity in the directions 0, 10", 20, 300, 00, 50 is represented (in Fig. ll) by O A, O B, O C, t.) D, O E, O F. l now calculate the mean luminous flux per surface unit, which is le +475 and deduce the intensity to be obtained in the vertical direction (00) which is the basis for determining curve 1%. This is readily determined by the rule of the cube of the cosine above indicated, and I may now trace the curve I), for uniform lighting upon the operative plane; the calculated intensity of the light in the directions 00, 100, l20", 30, a0", 50O should be O A1, O B1, O C1, O El, O F1. I then determine the elementary luminous flux corresponding to these intensities, that is I multiply such intensities by the area of the spherical Zone (whose radius is one unit of length) corresponding to the directions 00, 100, 200 etc., in consideration, comprised in a cone whose angle is for example 2 60O=120O (which is an arbitrary angle). I now compare the theoretical flux thus calculated with the flux actually measured (by the methods of Rousseau, etc., as above explained) and I find that the actual f flux contained in the upper hemispherical re- Direction 0 5 Intensities 1n candles 0 0 Direction 95 Intensities in candles 130 spherical .regions the flux of the upper regions in order to compensate as exactly as possible such deficiency. v

In the present example, the maximum intensity or" the lamp without external reflectors being emit-ted at (Fig, 11) I will obviouslyl place the lower edge of the lowermost reflector E1 above the 55 radius, for example on the radius .y

Suppose I desire to provide three reectors or screens El, E2, E3 and that the lowermost screen E1 is arranged to intercept the flux emitted in the region 60-800, that is 2064-1482354 lumens, the second screen intercepting the flux in the region 80410", that This corresponds tovectors O A, 0 B, etc., is 13G-l- 142l159=437 lumens, and the upin curve P4. p

The corresponding fluxes, deduced therefrom are as follows Half-angle of the cone 0. 10 20 to to to 10 20 30 Area in the sphere" 0,095 0,283 0,463

Flux in luxueus--- 0 4 32 Halfangle of the cone 90 100 110 to to, to

Area in the sphere 1,091 1,057 0,992

Flux in lumens 142 159 150 These intensities are represented by O A1, O B1, O C1, etc. A

The theoretical elementary fluxes deduced therefrom are:

Half-angle of the cone t0,

o 10 Area in the sphere 0,095 Flux in lumens 1a The total fiux 'is the sum, that is v1451 lumens. Since the actual measured flux is 1987, this corresponds to an efficiency of' 1451+1987=0,73 for the external reflectors, which is reasonable.

The comparison between the actual flux and the theoretical' fluxv'to be obtained is shown hereunder (Ionical regions Flux of the lamp alone Theoretical flux 01": the optimum lamp Differences The differences represent the deficiency in flux for the lower conical regions.

The external reflectors of the lamp should beso designed as to deflect into the lower permost screen intercepting the flux in the region 11G-180, that is to t0 to to to to 40 50 60 70 80 90 0,028 0,774 0,897 0,992 1,057 1,091 74 162 324 206 148 136 130 140 150 160 170 to to to to to to 140 150 160 170 180 lumens. The screens will thus intercept 354+487+600=1391 lumens, while the total deficiency of the lower 4cone whose angle is 120o is 15 +46-l-67-l- 108+ 188 -ll131:855 lumens., that is an efficiency of for the screens.

15 Y 25 35 45 55 1.11 1.31 V1,32 2.84 5,28 17e 214 20o 451 v:540

I then distribute the 855 necessary lumens between the three screens in proportionto the flux which they intercept (354, 43T, 600) that is: the screeny E, will reflect if,

Y 10D 20 a0n 40 a0 10 l to lo lo to 20 30 40 50 00u 0,233 0.403 0,028 0.774 0,807 50 00 isa 350 755 354 0,62=220 lumens, the screen E2 will reflect 437 0,62=270 lumens, the screen E3 will reflect 600 0,62=375 lumens.

If the screen E1 is arrangedv to reflect the light in the region 0480), it wiill largely compensate fort-he deficiency of this region (15-l-46-l-,67"=1281). The screen E2 is arranged to reflect Athe light in: the region A 0 4 32 74 162 324 15 50 99 182 350 755 15 l0 67 108 18S 431 S50-50, thus almost entirely compensating for the deficiency therein (108+188- r296.), and the screen E3 is arranged to reflect the light; in the region 50-60, thus almost completely compensating for the deficiency therein (431). In fact screen E1 is somewhat too large and screens E2 and E3 too small but the approximation is quite sufficient in practice.

The upper edge 4 of screen E1 is thus located on the 8OO radius, at a suitable distance from the lamp in order to prevent overheating of the screen and to keep the size of the apparatus within areasonable limits. Its lower edge 5 is at the intersection of the radius G00 with the first ray R reflected at 30 by the second screen E2 (in order not to intercept said ray) at point 4a, situated at a suitable distance from the lamp on the radius 110. The tangent to the screen at the different points is the perpendicular to the bisectrix of the angle formed by the incident and reflected rays. The intermediate points and tangents are determined by dividing the incident cone (iO-80 and the reflected cone 0-30o into an equal number of elementary regions.

'lhe upper edge of screen E2 being at 4a on the radius 110, its lower edge is at the intersection of the first ray R1 reflected at 50o by screen E3 at point 4Z) situated' at a suitable distance from the bulb on the radius 165O (the last ray having an appreciable intensity). The several points and tangents of' screen E2 are obtained as for screen El.

Screen E3 will extend from point 4Z) to a suitable point of the radius 1100, such as to keep the size of' the apparatus within the desired limits and by taking account of the general shape of the curve constructed point by point, with the tangents, as explain-ed with reference to screen El.

It will be observed that the use of the lamp with internal screen is essential for the economical distribution of the light upon the plane to be illuminated for the following reasons:

(a)'1`he screen Q entirely occults the light with respect to the surface to be illuminated within a cone whose angle at the vertex is 400. Since the amount of light to be reflected into the said cone in order to obtain a uniform illumination of the plane to be illuminated is very small (inasmuch as the illumination required in the vertical direction is only l/S of the illumination required at 60 from the foot of the vertical) the screen E1 which provides for the illumination on the plane to be illuminated between 0 and 3()o will reflect only a small portion ofthe total luminous flux emitted by the illuminant.

(b) The screen 2 concentrates the rays emitted inwardly within the loop 0r circle Vformed by the filament, as shown in Fig. 4, and reflects these rays at a mean angle of 550, that is in the direction (in the present ex ample) where the maximum luminous flux is required.

The reflecting screens E1,E2,E3 may consist of polished or enamelled metal or of opal glass or silvered glass. The number and the shape of the internal and external screens shown in the drawings are given solely by way of example and-may be varied as desired. The internal screen may be so arranged as to reflect the light emitted by the illuminant in any direction other than the one indicated in the drawings.

Obviously, the said screens may be secured in place in any suitable manner, and for instance by means of a fitting 6 mounted on the lamp, and provided with lugs 7, or in any other suitable manner.

Electric lamps such as herein described may be used as reflectors, or as difiusers for direct or indirect lighting.

In order to obtain a practically uniform illumination at all points of an elongated rectangular surface, the polar curves of luminous intensity should have the general shape shown in Fig. 12, in which 11 denotes the curve of luminous intensity longitudinally of the rectangle and 12 the curve of luminous intensity in the transverse direction.

The apparatus shown in Figs. 13 and 14, in which the said curves are obtained, comprises a trough-shaped external reflector 13 which is open at the bottom and is mounted on a vertical main body 14, secured to the cast iron cap 15 into which is screwed the tube 1G serving to support the apparatus.

The shape of the reflector has been specially designed to obtain the maximum spreading of the upper hemispherical luminous flux emitted by the lamp, as well as a distribution of the intensity according to curves 11 and 12. The said reflector may consist of an enamelled steel plate, or of polished, silvered or chrome-covered metal forming a mirroi: or of silvered glass, or glass provided with reflecting prisms by which the light can be sent in the desired direction.

The trough-shape of the reflector shown in the drawings is given solely by way of example, and any other suitable shape may be employed.

The apparatus comprises a tube 17 lslidable in the tube 1G, in which it may be held at any point by a set screw (not shown) said tube carries at the lower part a socket 18. in which is mounted the lamp 19, so that the lamp lilament can be vertically adjusted with reference to the external reflector.

Figs. 15 and 1G are views on a larger scale showing the arrangement of the lamp 19 and the reflector 13. A glass or metallic mirror 20 is placed in the lamp bulb below the said fila\ ment, and its shape is such that the light from filament 21 will be reflected in the proper direction. i

As shown in Fig. 16, the mirror Q0 comprises two oppositely disposed cylindrical reflecting surfaces, and the parts of the incandescent filament Q1 of the lamp are parallel with the respective faces of the reflector 20, so that each point of the said filament acts as a point source of light with respect to the adjacent portion of the screen; the filament will thus occupy with reference to the refleeting screen a position offering a uniform distribution of the light upon the whole width of the screen, whereby the Vwhole length of the incandescent filament will be availed. y

The filament 21 may consist of a continuous spiral, shunted to the electric circuit, or of two spiral parts mounted in parallel on the said circuit in such manner that if one part should become broken, the illuminant would not be completely extinguished.

A screen 22, placed above the filament, serves to reflect a part of the light produced in the upper hemisphere of the electric lamp, so that the light will not be absorbed by the main body 14 of the reflector 13.

The screen 22, as well as the screen 20, may consist of opal or silvered glass, or of glass comprisingr reflecting prisms, or of polished metal which is silvered or covered with chrome to form a mirror, or. like reflecting surface.

The shapesv of the screens shown in the drawings are given solely by way of example, and I may employ any other suitable shape.

.F rom the preceding considerations it will be observed that, by the combination of the lamp 19 with directed light with the reflector 13, I obtain upon an elongated rectangle a practically uniform illumination with a limited number of illuminants.

It is obvious that the details herein described and-represented are given solely by way of example; for instance the shape of the internal screen is not limited to the shapes illustrated in the drawing; its section may be plane, spherical, hyperbolic or the like. It may consist of opal glass, for example a double glass with the transparent part towards the filament, the opal layer being more or less opaque according to the amount of light which is to pass through (diused light), or it may consist of silvered or chrome-covered glass, or of glass covered with any reflecting metal. It may also consist of reflecting prisms of glass, or of a polished metal mirror.

The shape of the filaments is not limited to the shapes represented in the drawings, and they may have a zigzag or a saw-tooth shape, or the like. I may also employ several superposed filaments, or filaments placed in parallel layers, or filaments which are vertical or inclined from the vertical. i

In like manner, the number and the position of the said screens in relation to the filament may also be varied at will.

Obviously, the present invention is not limited to the constructions hereinidescribed and represented, which have been given solely by way of example.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In combination with an incandescent electric lamp having an internal reflecting member which is centered optically with respect to the filament and produces a concentration of the luminous flux in predetermined directions, external reflecting means adapted to deflect the luminous rays emitted by said lamp toward the plane to be illuminated with such a concentration of luminous flux that the intensity of light in each direction is inversely proportional to the cube of the cosinus of the angle formed by said direction with the perpendicular to said plane.

2. An incandescent electric lamp as claimed in claim 1, wherein said internal reflecting member is placed below said filament whereby it conceals the latter and directs the major part of the luminous flux upwardly, said external reflecting means being placed above said filament.

3. An electric incandescent lamp for the illumation of an elongated rectangular plane surface which comprises a bulb, a filament within said bulb having two incandescent portions whose general direction is parallel with the small sides of said rectangle, an internal reflecting member within said bulb, having two symmetrical reflecting surfaces of cylindrical shape parallel with and facing said incandescent portions respectively and centered optically with respect thereto, whereby two main pencils of light, of deter mined inclination, are directed toward the small ends of said rectangle, and means, outside said lamp, for reflecting the remaining light toward said rectangle, whereby a uniform illumination of the latte-r is produced.

4. An electric lamp as claimed in claim 3, wherein said reflecting means comprise an inverted trough-shaped reector which is elongated in a direction at right angles to the incandescent portions of said filament.

5. An electric lamp as claimed in claim 3, which further comprises an upper reflector within said bulb and above said filament,

kfor reflecting laterally the light emitted by the filament upwardly.

6. In an electric lamp as claimed in claim 1, means for adjusting the position of said lamp with respect to said external reflecting means.

7. In an electric lamp as claimed in claim 1,'a rod slidable with respect to said external reflecting means for carrying said lamp, and means for securing said rod in adjustable position with respect to said external reflecting means.

In testimony whereof I have signed my name to this specification.

GEORGES MAIN. 

